The hobby of making and flying high-performance realistic models of airplanes is very popular in the United States and elsewhere. Such model aircraft typically are radio-controlled, can be made to perform impressive maneuvers and stunts, and are propelled by wood, metal or composite material propellers driven by two-stroke or four-stroke internal combustion engines.
For many years modellers with machining abilities have tried to develop a true two-cycle multi-cylinder engine, sharing a common crankcase by using known art. Although some of the engines ran, the energy used to charge the crankcase left little energy to drive the propeller. These engines were impractical and unacceptable.
A typical two-stroke engine is one in which each complete rotation of a rotatable crankshaft corresponds to two strokes (one forward, one back) of a reciprocating piston connected to the crankshaft by a connecting rod, with one power stroke for every complete rotation of the crankshaft. A simple four-stroke engine also employs a piston and a connecting rod to rotate a crankshaft, but there is only one power stroke for every two complete rotations of the crankshaft. For the same size/weight, the two-stroke engine generates a higher power output than a four-stroke engine and is therefore sometimes preferred.
A multicylinder four-stroke engine may have a plurality of cylinders in-line, in a V-arrangement, opposed, or in a radial array relative to a common crankshaft axis. Each cylinder and piston arrangement requires respective intake and exhaust valves, and associated shared camshafts or the like to operate the valves in specific sequences. A single carburetor is typically employed, especially for a small engine, to provide a controlled mixture of air, fuel and oil to the cylinders. Lubrication for the moving parts in a four-stroke engine is typically provided by blow-by, i.e., by residual oil in the cylinders which passes by the piston into the crankcase, or by a sump providing oil for internal lubrication. In the radial configuration, when the engine stops the lower cylinders collect the oil from the crankcase. This requires the removal of the lower plugs, to prevent fouling of the plugs and hydrostatic lock.
A two-stroke engine, by contrast, typically has only one cylinder driving one rotatable crankshaft substantially encased within a crankcase. A mixture of vaporized fuel, air, and a lubricant in the form of very fine droplets is contained in the crankcase under pressure produced by the piston traveling downward into the crankcase. During the "down" stroke the piston passes the exhaust port, expelling the exhaust of the previous cycle. The piston upon traveling further downward a very short distance exposes a valveless intake port. The Pressurized fuel, oil, air mixture passes from the crankcase into the top of the cylinder, replacing the exhaust gas which continues to pass out of the exhaust port. On the second or "up" stroke the piston passes the intake and exhaust ports, sealing them from the crankcase. A vacuum is thus created in the crankcase while, simultaneously, a pressure is being created at the top of the cylinder. Fresh air/fuel mixture enters the crankcase through a carburetor and, as the piston reaches top dead center (TDC), an ignition source fires the compressed air/fuel mixture, generating a power stroke during which compressed products of combustion force the piston to make a working or power stroke. The connecting rod and the connected crankshaft thus are moved into their respective power-producing motions.
Although it is possible to have two two-cycle cylinder assemblies in a single crankcase, both pistons must reach top dead center at the same time and must also travel downward at the same time in order to create the pressure and vacuum necessary to operate the engine. This need to continually generate vacuum to draw fuel/air/lubricant mixture into the crankcase and generate compression needed to charge the cylinders is why multi-cylinder two cycle engines with a firing order, i.e., where each cylinder fires independently and alternately of the others, are not known.
It is well-known in the mechanical engineering arts that a two-stroke engine has fewer parts, needs little or no maintenance, and provides a higher power-to-weight ratio than does a comparably sized four-stroke engine.
The now historic great aircraft of "World War One" and "World War Two" and many commercial and private aircraft used radial engines. Even today, some aerobatic aircraft use radial engines. There has, therefore, for a long time existed a strongly felt need among model aircraft enthusiasts and the like for a multi-cylinder two-stroke engine which would be affordable, simple to operate, light in weight, relatively quiet, and capable of providing a high power to weight ratio. Serious modellers take great pains to ensure realism when building scale models and seek such a power source to enhance the realism and performance of their aircraft.
The present invention is intended to meet all of these needs, and differs in many significant respects from what is known in the prior art.
Thus, for example, U.S. Pat. No. 4,957,072, to Goldowsky, titled, "Balanced Radial Engine", provides a multicylinder radial aircraft engine in which an even number of individual single-cylinder, slider crank, two-stroke engines operate in opposed pairs in an integrated assembly. The outputs of the individual engines cooperatively drive a central common crankshaft via gears, but each engine obtains its air/fuel/lubricant mixture from its own individual crankcase. The disclosed composite engine, therefore, is really only an assembly of single-cylinder, two-stroke engines each with its own crankcase positioned to be radial in its individual (not common) plane about the rotation axis of the shared power-delivering crankshaft.
U.S. Pat. No. 5, 150,670, to Sadler, titled "Radial Internal Combustion Engine", teaches a four-stroke engine in which a plurality of paired rows of cylinders are disposed in respective common planes and the corresponding reciprocating pistons move within the cylinders to drive a common crankshaft.
U.S. Pat. No. 2,671,983, to Roehrl, titled "Toy Airplane", teaches a plastic toy airplane structure having ground contactable wheels. A child playing with the toy may move it in contact with a floor to drive, via gearing, a master connecting rod snap-fitted by a C-shaped slot to the crank pin of a crankshaft in a transparent plastic motor which allows the child to see the drive to a plastic propeller. The master connecting rod is connected to a piston and, via other C-shaped slots, is fitted to a plurality of other connecting rods which move respective pistons inside corresponding cylinders radially of the crankshaft axis. This, obviously, is merely a toy and the patent does not teach a functioning common crankcase or the like in a power-producing engine.
U.S. Pat. No. 2,312,661, to Messner, titled "Supercharger for Model Motors", teaches a fixed vane, friction-driven, rotating supercharger to improve combustion in a small internal combustion engine suitable for a model aircraft. The type of supercharger disclosed in this reference, while it may improve the power output and/or efficiency of a given single-cylinder engine, cannot provide an airflow and pressure augmentation that would be adequate for a multicylinder two-stroke engine.
U.S. Pat. No. 2,463,933, to Adkins, titled "Supercharging the Crankcase of Two-Cycle Engines", teaches a supercharger in which a slotted rotor holds a movable vane having an outer edge sliding along an eccentrically centered wall of a supercharger housing to provide pressure augmentation in a single-cylinder two-stroke engine. The inside end of the vane is spring-biased against a base of the slot within which the vane slides with its outer edge biased to maintain contact with the internal surface of a housing.
Thus, although there is considerable prior art relating to two- and four-stroke engines, etc., none is considered any more relevant to the present invention than the art discussed above.